A lazy eye (amblyopia) ideally needs to be diagnosed and treated as early as possible, preferably before a child is six years of age.

However, it can be difficult to know whether a child has a lazy eye because they often do not realise that there is anything wrong with their vision. Therefore, a lazy eye may not be diagnosed until your child has their first eye test.

Routine eye test

In the UK, children are usually given a routine eye test before they start school. This means that if a child has a lazy eye, it is possible to diagnose and treat the condition before it is too late to correct.

During their eye test, the structure of your child's eyes is examined to see if there are any abnormalities, such as astigmatism (where the surface of the lens is uneven, causing blurred vision).

Other tests include:

• in younger children who are unable to talk - covering each eye in turn to see if this makes them upset due to loss of their normal vision
• in children who can talk - a chart containing symbols of different sizes of objects such as a ball, a boat or a flower is shown to the child - they are then asked to name each object in turn until the object becomes too small for them to see; a significant difference between each eye would suggest a diagnosis of lazy eye
• in children who know their alphabet -  a similar test, that uses letters rather than symbols, can be used

If the eye specialist (ophthalmologist) suspects a lazy eye, a full eye examination will be carried out which will include each eye being tested separately for problems, such as long- or short-sightedness. Both eyes will also be tested together to see if there is a squint.